Headbox

ABSTRACT

A headbox construction for a papermaking machine which comprises a slice chamber connected to a preslice flow chamber by means of a perforate member. The slice chamber contains a plurality of plates and/or filaments attached to said perforate member and extend in the direction of stock flow through said slice chamber and define therein a multiplicity of relatively narrow channels of decreasing cross-sectional area in the direction of flow.

United States Patent Inventors Lester M. Hill Beloit, Wis.; Joseph D.Parker, Roscoe, 111.; Richard E. Hergert, Rockton, lll. Appl. No.698,633 Filed Jan. 17, 1968 Patented Sept. 21, 1971 Assignee BeloitCorporation Beloit, Wis.

HEADBOX 14 Claims, 17 Drawing Figs.

U.S. CL. 162/343 int. Cl DZlf 1/02 Field of Search. 162/336, 338, 339,343, 346, 347

References Cited UNlTED STATES PATENTS 2,394,509 2/1946 Boettinger162/343 6/1964 Robinson et al 3,272,233 9/1966 Trufitt 162/336 X2,832,268 4/1958 Boone et a1 162/343 FOREIGN PATENTS 236,864. 7/1925Great Britain 162/343 1,026,276 4/1966 Great Britain 162/343 PrimaryExaminer-Reuben Friedman Assistant Examiner-T. A. Granger Attorneys-Dirk.l. Veneman, John S. Munday and Gerald A,

Mathews HEADBOX This invention relates generally to a headbox for apapermaking machine, and more particularly to a headbox construction inwhich the slice chamber'includes a plurality of passages formed byelements in the direction of stock flow to uniformly direct stocktowards the slice opening at the downstream of said slice chamber.

in the Fourdrinier papermaking process, the principal difficulty inachieving uniform fonnation of a paper web is the natural tendency ofthe fibers to flocculate. An important feature of all Fourdriniermachine designs therefore is a means to disperse the fiber networksduring the period of sheet formation. At the present time, dispersion ofthe fiber network is effected by generating turbulence, used in thebroad sense, in the fiber suspension both in the headbox, frequentlythrough the use of rectifier rolls, and on the Fourdrinier table as aconsequence of the reaction of the free surface of the stock to thevariable acceleration over table rolls and foils. The dispersingactivity that occurs on the Fourdrinier table is an important supplementto the turbulence generated in the headbox and as a rule, the drainageon a Fourdrinier table is deliberately retarded to allow sufficienttreatment of the undrained suspension to obtain uniform fonnation. On aFourdrinier in which the table rolls have been replaced by suctionboxes, on the other hand, the fiber suspension is drained comparativelymuch more rapidly with considerably less activity generated in theundrained suspension. It follows that the formation of the sheet formedon a suction box or flat box Fourdrinier is much more sensitive to thecharacteristics of the headbox discharge 'that that of a conventionallyformed sheet.

A basic limitation in headbox design has been that the means forgenerating turbulence in fiber suspensions in order to disperse themhave been comparatively large-scale devices only. With such devices, itis possible to develop small scale turbulence by increasing theintensity of turbulence generated. Thus the turbulence energy istransferred naturally from large to small scales and the higher theintensity, the greater the rate of energy transfer and hence, thesmaller the scales of turbulence sustained. However, a detrimentalefiect also ensued from this high-intensity large-scale turbulencenamely the large waves and free surface disturbance developed on theFourdrinier table. Thus a general rule of headbox performance has beenthat the degree of dispersion and level of turbulence in the headboxdischarge were closely correlated; the higher the turbulence, the betterthe disperslon.

In selecting a headbox design under this limiting condition then, onecould choose at the extremes, either a design that produces a highlyturbulent, well-dispersed discharge, or one that produces alow-turbulent, poorly dispersed discharge. Since either a very highlevel of turbulence or a very low level (and consequent poor dispersion)produces defects in sheet formation on the Fourdrinier machine, the artof headbox design has consisted of making a suitable compromise betweenthese two extremes. That is, a primary objective of headbox design up tothis time has been to generate a level of turbulence which was highenough for dispersion, but low enough to avoid free surface defectsduring the formation period. it will be appreciated that the bestcompromise would be different for difi'erent types of papermakingfurnishes, consistencies, Fourdrinier table design, machine speed, etc.Thus a universal headbox design with presently available devices andtechniques would be difficult, if not impossible to establish.Furthermore, because these compromises always sacrifice the bestpossible dispersion and/or the best possible flow pattern on theFourdrinier wire, it is deemed that there is a great potential forimprovement in headbox design today.

The defects in sheet formation as a result of these extremes in headboxdesign, i.e., very high or very low turbulence, are even more markedwhen an a Fourdrinier is used wherein all table rolls and foils arereplaced by suction boxes. Thus when the turbulence is very low, as forexample in the discharge from a conventional rectifier roll-typeheadbox, the formation of the sheet formed by the rapid drainage oversuction boxes in the absence of the table roll activity directlyreflects the poor dispersion in the discharge jet. On the other hand,when the turbulence is very high, a wave pattern is generated in thefree surface of the flow on the wire as a consequence of the turbulence.With rapid drainage of the suspension in this case, the formation of thesheet reflects the mass distribution pattern of these waves. In additionto the free surface wave patterns, excessive turbulence may also entrainair and disrupt the thickened fiber mat which had been deposited earlierand cause formation defects.

Thus not only are the present extremes of headbox characteristicsunsuitable, but it is also difficult to find a suitable compromise for asuction box Fourdrinier application.

The unique and novel combination of elements of the present inventionprovide for delivery of the stock slurry to a forming surface of apapermaking machine having a high degree of fiber dispersion with a lowlevel of turbulence in the discharge jet. Under these conditions, a finescale dispersion of the fibers is produced which will not deteriorate asthe turbulence decays away; at least it will not deteriorate to theextent that occurs in the turbulent dispersions which are produced byconventional headbox designs. It has been found that it is the absenceof large-scale turbulence which precludes the gross reflocculation ofthe fibers since flocculation is predominately a consequence of smallscale turbulence decay and the persistence of the large scales.Sustaining the dispersion in the flow on the Fourdrinier wire then,leads directly to improved formation.

The method by which the above is accomplished, that is, to produce finescale turbulence without large scale eddies, is to pass the fibersuspension through a system of parallel channels of uniform small sizebut large in percentage open area. Both of these conditions, uniformsmall channel size and large exit percentage open area, are necessary.Thus the largest scales of turbulence developed in the channel flow havethe same order of size as the depth of the individual channels and bymaintaining the individual channel depth small, the resulting scale ofturbulence will be small. It is necessary to have a large exitpercentage open area to prevent the development of large scales ofturbulence in the zone of discharge. That is, large solid areas betweenthe channel's exits, would result in largescale turbulence in the wakeof these areas.

In concept then, the flow channel must change from a large entrance to asmall exit size. This change should occur over a substantial distance toallow time for the large-scale coarse flow disturbances generated in thewake of the entrance structure to be degraded to the small-scaleturbulence desired. The walls defining the channels immediatelyfollowing the entrance structure should be stiff enough to resistdistortion and fluctuation by these coarse flow disturbances andconsequent dynamic pressure variations. For this reason, it is importantfor the entrance to have a reasonably large open area to avoidunreasonably large downstream pressure fluctuations. Thus the more thecoarse turbulence in the flow channel is degraded toward a fine scale,the less stiff the channel walls need be to resist distortion. A simpleway of achieving stiffness is by increasing the thickness of the channelwall and this is the type of construction used at present as will behereinafter described in detail. Since it is therefore desirable for thechannel walls to progress from stiff thick members at their upstreamends to thin members at their downstream ends, the structure forconditioning the flow should consist of gradually converging channelsdefined by walls which simultaneously slowly converge and graduallydecreases in stiffness. Thus the simultaneous convergence of the channelsize and the walls defining the channels are complementary effects.Because of the diminishing channel depth, the pressure fluctuations arereduced to smaller scale and hence lower intensities which allowsthinner walls to be used to define the channel. Because of thediminishing wall thickness, the area between channels approaches thesmall dimension that it must have at the exit end. This concept ofsimultaneous convergence is deemed to be an important concept of designof this invention. While the preceding the slice opening S should be inthe order one eighth inch or smaller and the size of the solid areasbetween the channels at their exits should be much smaller than the sizeof the channels themselves. The exit open area should therefore bepreferably in the order of at least 80 95 percent. However, open areasin the order of'50 percent and larger are conceivable. In order toprevent plugging of the entrance portion of the slice chamber it isdesirable to maintain the vertical dimension of each of the channels 29,30 and 31, etc. at the upstream end in the order of I inch andtheoverall open area of the perforated plate should preferably be greaterthan percent. However, as a general rule the openings in the distributorshould be as small as possible for maintaining the flow pattern smallbut large enough to avoid plugging. These criteria will vary with theparticular application and stock characteristics.

It has further been found desirable to impart some flexibility to thedownstream end of the trailing members 25, 26, 27, etc. This flexibilityprovides a convenient way to achieve the small uniform spacing ofthemembers across the width of the slice chamber at the downstream endsince this uniform spacing is a hydrodynamically stable condition forthis particular structure as indicated by experiments. Thus, flexibilityallows the trailing members to be positioned by the dynamic forces offlow; that is, to conform to the streamlines. Alternatively, it would bedifficult to achieve uniformly spaced rigid trailing members withoutmounting the members to the sides of the slice chamber and even then itwould be difficult.

It is also desirable to impart some flexibility to the trailing membersto allow the passage of large particles which are inevitably present ina commercial stock-flow system. It is therefore a feature of the presentinvention not to have the trailing members attached to the sides of theslice chamber since this simplifies the construction and avoids a thinrigid channel which would be conductive to plugging by fibers andforeign matter.

In operation, papermaking stock is introduced into the tapered inlet 12through entrance opening 120. A portion of the stock enters orifices13a, 13b, 130, etc. while the remaining portion exits the tapered inlet12 through opening 12b for recirculation. From the orifices 13a, 13b,13c, etc. the stock enters the diffusers 14a, 14b, 140, etc. by means ofwhich the stock is uniformly distributed across the full width of thepreslice chamber 11b. The distribution of stock across the width of thepreslice chamber is of a coarse nature having a scale of turbulence orvariations in the order of a few inches. The coarsely distributed stockis then forced through the perforations in plate 15 by means of whichthe scale of turbulence is somewhat reduced but remains far above thedesired level for formation of a web. The stock then enters the channels29, 30, 31, etc. under conditions of relatively coarse and intenseturbulence. The upstream ends of the trailing members are supported bythe plate 15 and they are strong enough to accommodate the relativelylarge scale and intensity of the turbulence in the stock. As the stockprogresses through the channels, the cross section of which decreasesgradually, the intensity and degree of turbulence is likewise decreased.At the downstream end and near the slice portion S the channels arenarrow and bounded by flexible walls. At this end the scale ofturbulence has been diminished to acceptable papermaking standards. Thisdiminishing turbulence is accomplished by reducing the channel sizewhile still allowing coarse particles to pass by reason of theflexibility of the trailing members defining the channels. Theturbulence of the stock, therefore, in the channels is continuallydegraded from a coarse intense condition to a fine-scale low level. Thewalls of the channels are graduated in thickness and stiffnessaccordingly. The ultimate scale of turbulence in the flow from thechannels is governed by the size of the channels near the downstreamend, and the intensity is determined by the velocity of flow through thechannels which in turn is determined by the number of channels. In thismanner the scale and intensity of the discharge flow can beindependently controlled.

FIGS. 2 through 12 show additional details and other forms of thepresent invention.

As shown in FIG. 2 a headbox 40 of a somewhat simplified designcomprises a tapered inlet header 41 having an inlet opening 42 and anoverflow opening 43. The front wall of the header 40 comprises aperforated plate 44 having a multiplicity of perforations 45, 46, etc.therein. These perforations are preferably in the form of orifices andprovide for open communication between the inlet header and a slicechamber generally designated by the numeral 47. The slice chamber 47comprises top 48 and bottom 49 walls converging in the longitudinal ormachine direction and terminating at a slice portion S2. Appropriatetransversely spaced sidewalls are provided at the front and rear end ofthe slice chamber. Extending longitudinally within the slice chamber 47are a plurality of trailing elements 50, 51, 52, etc. One end of each ofthese trailing elements is attached to the perforated plate 44 at theupstream end of the slice chamber 47. The trailing elements extend forapproximately the full length of the slice chamber and are not attachedto any other part of the chamber other than at the perforated plate 44.

The trailing elements are thus permitted to float freely within theslice chamber with the exception of their restriction at the point ofattachment to the perforated plate 44. With papermaking stock flowingthrough the slice chamber the trailing elements willform a multiplicityof longitudinally extending flexible channels through which thepapermaking stock will flow thereby gradually reducing large-scaleturbulence in the papermaking stock while maintaining a high degree offiber dispersion. The thus-conditioned papermaking stock exits throughthe slice opening S2 and is deposited on the Fourdrinier wire 53 or onany other appropriate webforming surface. The Fourdrinier wire 53 issupported immediately beneath the slice by a roll 54, commonly referredto as a breast roll.

As shown in FIGS. 3 through 10, the trailing members may have differentforms each of which can be readily adapted to suit a particularoperating condition. For example, as will be readily apparent to thoseskilled in the art it may be more convenient to have the flexiblemembers 50, 51, and 52, etc. extend transversely of the slice chamber inthe form of a fullwidth sheet, as described in connection with FIG. I,where the transverse dimension of the preslice flow chamber isrelatively narrow. On the other hand, it will be apparent that inextremely wide headboxes it may be more practical to have a plurality ofrelatively narrow sheets extending in the transverse direction of theslice chamber. Accordingly, FIG. 4 shows the flexible trailing elementsextending transversely of the slice chamber with the flexible elementshaving approximately the same transverse dimension as the slice chamber.

As shown in FIG. 5 the transverse dimension of the individual trailingelements 60, 61, 62, etc. is reduced to a fraction of the transversedimension of the preslice flow chamber which may be a more practicalapproach for headboxes having a relatively large transverse dimension.

FIG. 3 shows a further embodiment of the present invention and it willbe noted that the trailing elements herein consist of a plurality offlexible rods or wires 63, 64, 65, etc. having a generally circularcross-sectional area. This embodiment is particularly useful where stockcharacteristics require the use of channels of extremely smallcross-sectional area.

As shown in FIG. 6, the longitudinal cross-sectional area of thetrailing elements 50, 51, 52, etc. is preferably made so as to have itscross-sectional area decrease longitudinally in the direction of flow.The decrease in cross-sectional area is commensurate with the decreasein cross-sectional area of the slice chamber 11a of FIG. I and 47 ofFIG. 2. In this manner the complementary effects of simultaneousconvergence of the channel size and the flexible elements are obtained.In the embodiment of FIG. 6 the transverse cross-sectional area remainssubstantially rectangular as shown in FIG. 7.

FIG. 8 shows the cross-sectional area of the trailing elements 50, 51,52, etc. of FIG. 3 and while this cross-sectional The whole was passedinto an oven at 150 C., and kept there for 1-2 minutes. Thereafter, ontothe previous layer a second layer (foamed) was spread. which consistedof:

PVC, paste making resin having a K-value of 72 dioctyl phthalate 100parts (by weight) 80 parts (by weight) The initial thickness of thislayer was 200 microns.

The whole was then passed into an oven at 200 C. and kept there for l-2minutes. The release paper was then removed. The system was thensubjected to a slight tension in order to facilitate the separation ofthose components that were incompatible with each other; then the systemwas coupled to a cotton jersey fabric (with the second layer adjacent tothe fabric), after preliminarily having spread on the fabric someplastisol of the first layer which served as a binder. Said couplingoccurred in about 1 minute in an oven heated to ISO-170 C.

The poromeric material thus obtained showed the following airtranspiration rates:

Pressure (mm. Hg)

The release paper was then removed and the system was subjected to aslight tension and subsequently was coupled to a jersey fabric made ofpolyamide fibers, the second layer being adjacent to the fabric afterpreliminary having spread on the fabric some plastisol of the firstlayer which serves as a binder.

The poromeric material thus obtained shows the following airtranspiration rates:

Pressure cm. of air (mm.Hg) hr. cm.

4U 80 60 121 I00 205 ISO 270 Example 3 100 parts (by weight) PVC, pastemaking resin with a

2. The structure of claim 1 wherein the transverse cross-sectional areaof said elements decreases in the direction of stock flow.
 3. Thestructure of claim 2 wherein the transverse cross-sectional area of saidslice chamber decreases in the direction of stock flow.
 4. In a headboxfor delivering stock to a forming surface, the headbox having a slicechamber and a slice opening, the improvement comprising a plurality ofrigid plates positioned in the slice chamber, each of said platesextending transversely of said headbox and projecting downstreamgenerally in the direction of stock flow, and trailing elements attachedto the downstream ends of said plates, said elements being attached tosaid plates only at their upstream ends with their downstream portionsunaTtached and constructed to be self-positionable so as to be solelyresponsive to forces exerted thereon by the stock flowing towards theslice.
 5. The structure of claim 4 wherein said elements are in the formof sheets extending transversely of said headbox.
 6. The structure ofclaim 4 wherein said elements are in the form of flexible rods.
 7. Thestructure of claim 7 wherein the transverse cross-sectional area of saidrods is triangular.
 8. The structure of claim 6 wherein the transversecross-sectional area of said rods decreases in the direction of flow. 9.The structure of claim 4 wherein the transverse cross-sectional area ofsaid elements decreases in the direction of flow.
 10. In a headbox fordelivering stock to a forming surface, the headbox having a slicechamber and a slice opening, the improvement comprising a plurality ofrigid members positioned in the slice chamber, each of said membersprojecting downstream generally in the direction of stock flow, meanssupporting said members only at their upstream ends at locations spacedgenerally perpendicular to the stock flow stream, and trailing elementsattached to the downstream ends of said members, said elements beingattached to said members only at their upstream ends with theirdownstream portions unattached and constructed to be self-positionableso as to be solely responsive to forces exerted thereon by the stockflowing towards the slice.
 11. The structure of claim 10 wherein saidmeans comprise tubes.
 12. In a headbox for delivering stock to a formingsurface, the headbox having a slice chamber and a slice opening, theimprovement comprising a trailing element positioned in the slicechamber, said element extending transversely of said headbox, meansanchoring said element only at its upstream end with its downstreamportion unattached and constructed to be self-positionable so as to besolely responsive to forces exerted thereon by the stock flowing towardsthe slice.
 13. In a headbox for delivering stock to a forming surface,the headbox having a slice chamber and a slice opening, the improvementcomprising a rigid plate positioned in the slice chamber, said plateextending transversely of said headbox and projecting downstreamgenerally in the direction of stock flow, and a trailing elementattached to the downstream end of said plate, said element beingattached to said plate only at its upstream end with its downstreamportion unattached and constructed to be self-positionable so as to besolely responsive to forces exerted thereon by the stock flowing towardsthe slice.
 14. In a headbox for delivering stock to a forming surface,the headbox having a slice chamber and a slice opening, the improvementcomprising a rigid member positioned in the slice chamber, said memberprojecting downstream generally in the direction of stock flow, meanssupporting said member only at its upstream end and trailing elementsattached to the downstream end of said member, said elements beingattached to said member only at their upstream ends with theirdownstream portions unattached and constructed to be self-positionableso as to be solely responsive to forces exerted thereon by the stockflowing towards the slice.